Preparation of polythioamides from thiolactams



Patented Mar. 10,1942

Norman L. Cox, Claymont, and William E. Hanford, Wilmington, DeL, assignors to E. r. 1111 Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February .9, 1940,

Serial No. 318,198

12 Claims. (01. 260-2) This invention relates to the preparation of polythioamides.

This invention has as an object the provision of a process for making polythioamides, more particularly polymeric amides of primary monoaminomonocarbothionic acids. A further object is the preparation of new polythioamide interpolymers. Another object is the preparation of materials of use in the manufacture of films, fibers, filaments, coating compositions, molding compositions, etc. Other objects will appear hereinafter. I

These objects are accomplished by the following invention wherein a thiolactam containing at least seven annular atoms is heated in the presence of a thioamide-splitting. catalyst to form a linear polythioamide.

In the process of the present invention, a suitable thiolactam and a catalyst (either alkali metal, water or other thioamide-splitting agent) are heated in by this process are characterized by their. rubbery properties which are maintained up to their melting points which are usually over 200 C.

In addition to the formation of straight, i: e.,

simple, polymers, the thiolactam method lends itself readily to the preparation of interpolymers, for example, by subjecting a mixture of two or more thiolactams to polymerization conditions.

Of particular interest are the interpolymers ob tained from mixtures of thiolactams with their oxygen analogs, the lactams. In general, inter polymerization of a thiolactam with 'e-caprolactam and other oxygen'analogs of larger ring size is carried out in the manner described in the previous paragraph. With e-caprolactam and e-thiocaprolactam (in proportions of 4:1 in particular) slightly colored, high melting polymers containing as high as 3.0% sulfur can be obtained by heating with water as catalyst at 180 for 150 hours. If a higher temperature is used, excessive decomposition occurs. The resulting tough product, which melts in the range 150200, is insoluble in mixtures of methanol efiected in 24 hours with sodium as the catalyst,

or 48 hours with water, whereas the conversion of the eight-membered thiolactam requires several days at the same temperature. A two-hour schedule for w-thioheptanolactam at 250 C. produced a polymer of approximatelythesame degree of polymerization as several days at 180 C.

It is preferable to use at least l/ 10 mol of water i or 1/100 mol of alkali metal per mol of cyclic thioamide. When sodium is used as catalyst,

is is better to carry out the initialreaction at a relatively low temperature (approx. 100-120" C.) to avoid charring. As soon as the sodium has many forms of the invention other than these disappeared the temperature may be raised to operating temperature. Sodium metal catalyst has been shown to materially shorten the time necessary to efiect a satisfactory degree of polymerization. After the heating schedule has been completed and the product cooled, it may be used.

and chloroform. If a larger proportion or e-thiocaprolactam is used, the product is less tough and may even be brittle. Very, satisfactory products are obtained with thiolactams containing more than 7 annular groups since these lactams are not so susceptible to thermal decomposition. These interpolymers constitute, so far as is known, the highest molecular weight polymers containing thioamide units, as shown by intrinsic viscosity determinations. Y

The more detailed practice of the invention is illustrated by the following examples, wherein parts given are by weight. There are of course specific embodiments.

Example I One part of w-thioheptanolactam,

NH and 0.0125 part ofwater are sealed in'a glass tube and heated at 180 for 7 days. The product, upon cooling to room temperature, sets up to a reddish-brown polymer. This product possesses thermoelasticity above room temperature, melts at 235 C. and has an intrinsic viscosity over 0.3 in m-cresol. By intrinsic viscosity? as applied to the polyis heated at 250 C. for 2 hours.

deformed with the fingers.

mers of certain of the examples, is meant the mathematical quotient losnNr C where Nr is the viscosity of a dilute (e. g., 0.5%)

' solution of the polymer in a suitable solvent (e. g., m cresol) at a convenient temperature (e. g., 25 C.) divided by the viscosity of the same solvent in the same units at the same temperature, and C is the concentration in grams of polymer per 100 cc. of solution.

Example II One part of w-thioheptanolactam is heated with 0.005 part of metallic sodium in a closed vessel at 180 for sevendays. The product obtained in this experiment is a viscous resin which softens below room temperature. viscosity is over 0.3 in m-cresol.

Example III Example IV To 0.5 part of w-thiocaprylolactam c=s i)1 in a tube is added 0.005 part of wateri the tube is evacuated to 5 mm. pressure and sealed while being cooled in an acetone-solid carbon dioxide bath, and is then heated to 180 C. for 48 hours. On cooling, a slightly colored solid is obtained, which has more toughness and less elasticity than that of: the preceding example.

Example V A mixture of 05 part of (ii-thiocaprylolactamand 0.004 part of sodium is heatedat 180 in a closed vessel in the usual manner. After 24 hours the product'sets up to a thick gel. The heating is continued for a total of 48 hours. The product is rather soft when first examined, but on standing in air it becomes so hard as to be diflicultly The solid softens above room temperature and maintains its elastic properties up to 300 C., at which point it melts.

Example VI e-Thiocaprolactam and a trace of BF:.3H2O complex are heated in a sealed evacuated tube at 180 for. 72 hours.

' The tube is cooled down. to room temperature and the contents removed without attempting to drive oil the residual monomer under reduced pressure. The product is a somewhat colored material which flows to the shape of its container. It possesses a certain elasticity. Its

molecular weight can be increased by further heating under reduced pressure but remains probably lower than that of the polymers derived from thiolactamscontaining more'than' seven annular atoms.

Its intrinsic Example VII A mixture of 0.5 part of w-thioheptanolactam, 2.0 parts of e-caprolactam, and 0.005 part of sodium is heated at 250 in an evacuated, sealed reactor for 150 hours. An elastic rubbery polymer is obtained which melts at 96 C. Its intrinsic viscosity is 0.38 in m-cresol.

' Example VIII A mixture of 9.0 parts of e-caprolactam,

/c=o (cm).

. NH 1.0 part of e-thiocaprolactam and 0.162 part of water (1 part of water to 10 parts of lactam based on combined weight) is heated in an evacuated,

' sealed reactor ior 144 hours at 170 C. The resulting polymer is then heated for 3 hours at 250 under reducedpressure. A cream-colored solid with melting point 212 C. and sulfur content of 0.55% is obtained. This material has a very high molecular weight as shown by its intrinsic viscosity of 1.23 in m-cresol, is insoluble in mixtures of chloroform and methanol, and can be'pressed intotough, water-resistant films.

Example IX To 8 parts of e-caprolactam in a tube are added 2.0 parts of e-thiocaprolacta'm and 0.16 part of water. The tube is evacuated, sealed and heated at 180 C. for 120 hours, at which temperature its, contents are solid. The product is further heated under'vacuum at 220 C. for 3 hours to remove the monomer. A cream-colored solid, melting at 207 0., containing 2.75% sulfur and having an intrinsic viscosity of 0.85 in m-cresol is obtained. Recrystallization from hot formamide or phenol does not change the sulfur content, indicating that interpolymerization had occurred. This product is insoluble in mixtures of methanol and chloroform and can be pressed into tough films.

In the process of the present invention, any thiolactam containing at least seven annular atoms can be polymerized using alkali metals, water, or any other amideor thioamide-splitting catalyst. The thiolactams polymerizable by this process include e-thiocaprolactams, w-thioheptanolactam, methyl thiocaprolactam, wthiocaprylolactam, 3-methyl thiocaprylolactam, w-

thiononanolactam, 4-methylthiononanolactam and its other substituted products, and w-thiodecanolactam. These thiolactams may be ob tained by any known method, as, for example, the rearrangement of the corresponding cyclic ketoximes with sulfuric acid and subsequent reaction of the lactam (isoxime) with phosphorus pentasulfide. e-Thiocaprolactam is prepared more conveniently by heating e-aminocapronitrile under pressure in alcohol saturated with hydrogen sulfide, as disclosed in Pinkney U. S. Patent 2,201,200 issued May 21, 1940, on copending application Serial No. 199,988. This process is also applicable to the polymerwherein R and R represent divalent hydrocarwhich may be obtained by treating with phosphorus pentasulfide, the corresponding oxygen compound, itself obtained as a by-product in the manufacture of polymeric hexamethyleneadipamide. The polymers prepared from these di(thiolactams) contain a mixture of recurring units in whichthe chains R and R may be of the same or different lengths.

In the present process wherein a thiolactam is rearranged, there may be employed mixtures of thiolactams, of thiolactams with lactams, and of thiolactams with cyclic esters, such mixtures comprising in effective amount a thiolactam of at least seven annular atoms. Thus the inventicn is applicable to the production of interpolymers such as those obtained by heating together e-caprolactam and E-thiocaprolactam. Any lactam, i. e., cyclic amide of'at least seven annular atoms may be employed including those derived by rearrangement with sulfuric acid of the oximes of cyclohexanone, methylcyclohexanone, cycloheptanone, cyclooctanone, cyclopentadecanone and cyclohexadecanone.

Likewise any cyclic ester, i. e., lactone of at least six annular atoms may be used, including caprolactone, heptanolactone, lactone of w-hydroxymyristic acid, etc.

The quantity of water used as amide-splitting agent in carrying out the polymerization is at least 0.1 mol per cent based on the thiolactam. Quantities of water considerably in excess of this lead to excessive degradation, while less than 0.1

mol of water is insufiicient to give ready polymerization. The preferred proportions of sodium metal as catalyst lie in the range 0.01 to 0.04 mol per mol of thiolactam. A temperature range of 160 to 260 C. may be used. A short heating schedule at 250 C. is usually as effective as a long heating schedule at 180 C.; however, the latter conditions are preferred, since high temperatures may give excessive decomposition. Other amideor thioamide-splitting agents in carrying out the process of this invention can be used; namely, acetic acid, ethanol. met anol, ammonium hydroxide, aqueous mineral acids, boron trifiuoride and others; alkali and alkaline earth metals such as lithium or calcium may be used. However, the temperature and heating time must be regulated according to the eiiec tiveness of the catalyst. Available data indicate that the ease of polymerization improves with increase in the number of annular atoms present in the cyclic compound.

The polymerizations and interpolymerizations may be conducted either in closed. evacuated vessels or in openvessels in the presence of an inert gas such as nitrogen. Polymerizations with water or other volatile catalyst must be carried out in sealed reactors to retain the catalyst, at least until a suificient degree of polymerization is reached. The product'at the end of the heating schedule is usually a rubbery, sometimes slightly colored, polymer which shows some tendency to adhere to glass.

caprylolactone,

The products of the process of this invention are linear polymeric secondary amides derived units chain between and including the amino nitrogen and the cyano carbon. The radical length of the polymer derived from a thiomonolactam corresponds to the number of annular atoms.

The products of the invention are the interpolymeric polythioamides containing the reaction residues of a plurality of thiolactams or of at least one thiolactam with at least one lactam and/or lactone by applying the process of this invention to a mixture of at least one thiolactam with at least one other thiolactam or at least one lactam or at least one lactone or a mixture thereof. They may be described as interpolymeric polythioamides of monoaminomonocarbothionic acids containing. a plurality of recurring HN-RCS-, wherein R contains a chain of at least five atoms, the interpolymeric polythioamides also being characterized in that they contain a plurality of recurring units selected from the class of the reaction residues of the thiolactams -HN-R C'S, la'ctams and lactones OR CO, wherein R is different from R and R. may be R or R The examples disclose the preparation of olymers or interpolymers of rad cal lengths of 7, 8, and 9, but the process of the invention is generic to the preparation of polythioamides derived from primary monoaminomonocarbothionic acids of the formula H.2NRCSOH, wherein R is a substituted or unsubstituted bivalent organic radical attached to the amino nitrogen by aliphatic carbon having a chain between and including the amino nitrogen and the thiocarbonyl carbon of at least seven, including the polythioamides which may be considered as derived from the following amino acids: w-aminocaproic ac d. w-aminocaprylic acid, w-aminononanoic acid, w-aminoheptadecanoic acid, 12- aminooctadecanoic acid. p-aminomethylbenzoic ac d. p-aminomethylhydroc nnamic acid, 10- aminodecanoic acid, Z-methyl-G-aminohexoc ac d. S-methyl-G-aminohexoic acid. -amino-M- carboxyd propyl ether and the like, as well as carbon substituted derivatives of the above. Unsaturated amino acids may be used. Completely aliphatic amino acids are preferred and of these the saturated acids are more desirable.

The polymers and interpolymers of the present invention may be used in the production of fibers, filaments, films and molding and coating compositions. Their rubbery properties make them particularly valuable for some applications, e. g., as modifying agents in polyamide resins to impart flexibility. The polythioamides of this invention are also valuable as lightand oxygenstabilizing agents in polyamides. The interpolymers are characterized by their high intrinsic viscosity, indicative of high molecular weight. Films obtained therefrom are resistant to water.

The above description and examples are intended to be illustrative only. Any modification 'ofor variation therefrom which conforms to the spirit of the invention is intended to be included within the scope of the claims.

Whatis claimed is:

1. Linear interpolymeric secondary amides of primary monoaminomonocarbothionic acids having a recurring structural unit NH RCS- wherein R is a divalent hydrocarbon radical having a chain length of at least five, and wherein the valence. attached to nitrogen stems from aliphatic carbon, and further characterized by having.a recurring structural unit of the class consisting of the reaction residues -NH--R CS of different thiolactams, the reaction residues residues OR -CO- or lactones, R and B of lactones, R and R. being divalent aliphatic hydrocarbon radicals, R being different from R.

3. Linear interpolymeric secondary amides of primary monoaminomonocarbothionic acids having a recurring structural unit ---NH.R--CS wherein R is a divalent saturated aliphatichydrocarbon radical having a chain length of at least five, and further characterized by having a recurring structural unit of the class consisting of the reaction residues --NH--R -CS of different thiolactams, the reaction residues of lactams, and the reaction of residues of lactones, R and It being divalent saturated aliphatic hydrocarbon radicals, R being difierent from R.

4. Linear interpolymeric secondary amides of primary moncaminomonocarbothionic acids having a recurring structural unit -NHR- -CS wherein R is a polymethylene radical having a chain length of at least. five, and wherein the valence attached to nitrogen stems from aliphatic carbon, and further characterized by having a recurring structural unit of the class consisting of the reaction residues --NHR -CS of different thiolactams, the reaction residues NHR CO of lactams, and the reaction residues O-R -CO of lactones, R and It being polymethylene radicals, R being difierent from R.

5. Linear interpolymeric secondary amides of primary monoaminomonocarbothionic acids having a recurring structural unit NH--R-CS wherein R is a divalent hydrocarbon radical having a chain length of at least five, and wherein the valence attached to nitrogen stems from aliphatic carbon, and further characterized by having a recurring structural unit NHR CS of a different thiolactam, R being a divalent hydrocarbon radical difierent from R.

6. Linear interpolymeric secondary amides of primary monoaminomonocarbothionic acids hav ing a recurring structural unit -NHRCS- wherein R is a divalent hydrocarbon radical having a chain length of at least five, and wherein the valence attached to nitrogen stems from aliphatic carbon, and further characterized by having a recurring structural unit NHR CO' of a lactam, R being a divalent hydrocarbon radical.

7. The interpolymer of e-aminocaproic acid and e-aminothiocaproic acid.

8. Linear interpolymeric secondary amides of primary monoaminomonocarbothionic acids having a recurring-structural unit wherein R is a divalent hydrocarbon radical having a chain length of atleast five, and wherein the valence attached to nitrogen stems from aliphatic carbon, and further characterized by having a recurring structural unit OR=C0- of a lactone, R being a divalent hydrocarbon radical.

9. Process for preparing linear polymeric secondary thioamides'whichcomprises heating a thiolactam of at least seven annular atoms and V thiolactam of at least seven annular atoms and is used as the catalyst, the reaction being conducted at 100-120 C. until the sodium is used containing, apart from thiolactam" sulfur and nitrogen, only carbon and hydrogen with an amide-splitting catalyst underpressure at 180- 250. C. until a linear polymer is obtained and isolating the polymer.

11. Process of claim 9 wherein metallic sodium up and thereafter at l-250 C.

12. Process for preparing linear polymeric secondary thioamides which comprises heating a thiolactam of at least seven annular atoms and containing, apart from the thiolactam nitrogen and sulfur; only carbon and hydrogen with a lactam of at least seven carbon atoms and containing, apart from the lactam oxygen and nitrogen, only carbon and hydrogen and with an amidesplitting catalyst under pressure at 250 C. until a linear polymer is obtained and isolating the polymer.

NORMAN L. cox I WILLIAM E. HANFORD. 

